Industrial wastewaters are generated as a by-product from industrial operations which include (but are not limited to) chemical manufacturing or processing, food and beverage production and the oil and gas industry. In the field of industrial or wastewater treatment, it is known to use advanced oxidation processes (AOPs) to treat water or waste water through interactions with reactive oxygen species such as hydroxyl radicals (.OH). Advanced oxidation processes are useful for a number of reasons, including the high reactivity of hydroxyl radicals and their applicability in oxidising a range of organic and inorganic contaminants; their ability to treat organic compounds directly when in an aqueous phase; and the absence of additional hazardous substances or waste streams.
One example application is in the treatment of produced water in the oil and gas industry. Produced water is a wastewater by-product from hydrocarbon extraction, and it must be separated from the oil and gas fractions of the produced fluid. The separated water will contain low but measurable amounts of organic and inorganic contaminants that have the potential to harm the environment and so the water must be treated. Another hydrocarbon industry application is the treatment of wastewater from hydraulic fracturing operations.
Examples of advanced oxidation processes include those in which oxygen (O2), ozone (O3), hydrogen peroxide (H2O2) and/or ultraviolet (UV) radiation are used to generate hydroxyl radicals in the reaction process, either alone or in combination with one another. Some advanced oxidation techniques use metal oxide catalysts such as titanium dioxide (TiO2) or aluminium oxide (Al2O3) in order to lower activation energies, lower ozone consumption, and/or ultimately to enhance reaction parameters such as the rate of reduction in Total Organic Content (or Total Organic Carbon) (TOC). Advanced oxidation processes have been engineered for batch treatment of liquids and continuous online treatment within flow systems.
A range of different factors are known to impact on the efficiency of an advanced oxidation process, and there is generally a demand to improve upon the efficiency of existing systems, process time, and the ability to handle a range of flow rates and contaminants.
GB 2,404,189 describes a process and apparatus for the treatment of produced water from the hydrocarbon production industry, which uses a combination of ozone and UV radiation to reduce hydrocarbon and organic matter within the water. A Venturi ozone injector is used to introduce and dissolve ozone into the produced water flow stream which is subsequently exposed to UV radiation.
WO 2012/056249 discloses a fluid treatment apparatus for an advanced oxidation process. The apparatus comprises a primary flow line connecting an inlet and an outlet of the apparatus and an ozone-injecting device. A reactor vessel includes a UV light source for treating the ozone-enriched fluid. A secondary flow line is arranged in parallel to the primary flow line to provide variation of a fluid flow rate within the apparatus.
While the approaches described in GB 2,404,189 and WO 2012/056249 are useful in certain applications to the treatment of produced water, there remains a commercial need to provide water treatment apparatus and processes which have improved efficacy, economy, reliability and/or flexibility of application.
Cavitation is the process of the formation of the vapour phase of a liquid within cavities or voids in the liquid phase, and occurs when the liquid is subjected to reduced pressures at constant ambient temperature. Hydrodynamic cavitation occurs when a device generates cavitation due to sudden changes in flow geometry, creating local reductions in pressure. Hydroacoustic cavitation is generated by the hydrodynamic generation of periodic changes in liquid pressure.
The implosion of cavities or voids generates intense shock waves. Although the collapse of a single cavity is a relatively low-energy event, localised cavitation is known to cause damage to flow components, pumps, propellers and the like. In particular, cavitation is known to produce pitting or erosion of metals, and has a significant effect on wear and damage on moving components. Although cavitation effects have been harnessed in some industrial cleaning applications, including scale removal and corrosion reduction, where the cavitation energy has been used to loosen adhesion between contaminants and flow surfaces in flow systems.
U.S. Pat. No. 4,906,387 describes a method and apparatus for oxidising contaminants in water, in which cavitation is induced by passing the water through a cavitation nozzle prior to irradiating the water with ultraviolet radiation.
WO 2005/021050 describes an apparatus and method for liquid treatment by a combination of irradiation (for example UV irradiation) and cavitation. The apparatus comprises a rotary cavitation device in the chamber of a reactor. Cavitation of the liquid is said to introduce a greater surface area of fluid in the radiation treatment zone, thereby increasing the rate of exposure of fluid to the radiation.